2) Pyruvate will enter the tricarboxylic acid cycle, be catabolised by pyruvate dehydrogenase into either Acetyl Coenzyme A or Ox.-Aloacetate. Then, the reduced nicotinamide adenine dinucleotide (NADH) and Succinate (C4O4) will enter an electron transport chain in oxidative phosphorylation to be oxidised, which is the most efficient way of releasing energy, unlike the glycolysis fermentation process.

1) Oxaloacetate is a compound (C4O5) in the tricarboxylic acid cycle, it is an isomer of Malate, after the action of Malate Dehydrogenase or Pyruvate Carboxylase, and is a compund which has been formed (sometimes oxaloacetate, sometimes acetyl, depending on the end compound that will be produced) after catabolism of pyruvate.2) Yes, it is only the carboxyl group, C4O4 succinic acid has 6 hydrogen atoms.3) Yes, oxidative phosphorylation, after a coupled reaction with Coenzyme Q to QH2 with the enzyme succinate dehydrogenase.

1) it's difference between Ox.-Aloacetate and oxaloacetate2) no, succinate is not C4O4, you're forgetting hydrogens 3) succinate doesn't enter the ETC. It just passes electrons to coenzyme Q, but otherwise is involved in TCA cycle, not in ETC

1. Sorry, I intended to type Oxaloacetate, not "Ox.-Aloacetate".2. Sorry, I mistyped that, obviously succinic acid is C4H6O4.3. Yes, succinate does pass electrons to Coenzyme Q (Q to QH2) but I thought you were referring to it entering "a stage" of oxidative phosphorylation, not primarily the electron transport chain.